"the keyer buffer stayed full for 4s" and nothing keyed, on a rig whose CAT is
working. The buffer was not full: the check demanded the reply be exactly "KY0;"
with the digit at byte 2, so anything the FTDX10 phrases differently — a space
before the digit, another command's reply arriving first — read as "still full"
on every poll until the deadline.
The test is now asymmetric on purpose: only a clear "1" holds the send back.
Anything unrecognised goes ahead. Refusing to transmit because a status line was
phrased unexpectedly is the worse failure — the operator gets silence with no
explanation, where at worst sending early truncates a long message, which the
chunk loop then recovers from.
The reply is also logged once per run, since we have no verified sample of it —
that line is what turns the next surprise into a fact instead of a theory.